Importance of Reactive Power in Power Systems

Reactive power represents basic signals which are present in all alternating voltage installations, due to their nature and specificity, although they do not produce directly useful effects (light, heat, mechanical work, etc.). Most of the time, the realization of useful effects is not possible without reactive energy consumption, taking into account the magnetization processes that take place in motor drives iron cores, and electrical transformers.

Also, the leakage fluxes corresponding to the electric lines and to the coils determine reactive power consumption. The resistors, used as electrical energy receivers, consume only active energy, but its transfer through the installations placed upstream reactive determines the energy and reactive power losses.

In general, one can say that in nowadays electrical systems, active energy, and active power management take place only in the presence of and with a big consumption of reactive energy and reactive power. From here it results also in the concern that the problems corresponding to producing and management of reactive power and reactive energy to be examined simultaneously with those related to active power and under higher efficiency taking into account their corresponding specificity. At the same time, one should notice also the signal that expresses the correlation between the two powers and energies categories which is the power factor PF, as the main signal for guiding the analysis of the corresponding problems.

As a general aspect for reactive power and reactive energy management in electrical installations, one considers as necessary, to underline the essential difference between the process required to produce active power and active energy that takes place, in principle, in electric power plants, belonging to the energetic system and the one corresponding to producing reactive energy and reactive power. This is because active energy production implies primary energy consumption, which is not the case for reactive energy, except the case for covering some active energy losses, reduced as signal.

The necessity to have a reactive power flow control arises from the fact that, practically, in each station, for solving sinusoidal states, the adopted solution is that of using capacitor banks. These are installed, usually, on low voltage mains power supply of the transformer power, which are connected the consumers from all or from a part of the enterprise. The purpose, with priority, is to obtain an overall power factor, at least equal to the neutral value (imposed by the electrical energy provider contract), in the point used for measuring the active and reactive energy consumption of the electrical installations, placed downstream, avoiding the overcompensation situations. In general, for the energy provided to the consumers, the values obtained for the overall power are in the 0.93 … 0.97 range.

Many factories use also automatic multi-step power factor correction systems, to maintain constant value for the power factor. This is the situation for long-term functioning in industrial installations, on the occasion of the current jobs. One can affirm this solution contributes to rational management of the reactive energy and reactive power, representing a priority in the electrical energy sector.

The analysis of this aspect is done, in general, at the enterprises level, because the electrical energy consumers from this one, and especially the operation, with very large nominal power range, sometimes due to over-sizes, as well as the corresponding low-loaded functioning, have the biggest weight from the general reactive power consumption, sometimes up to 60–70%.

The transformers from the electroenergetical system take around 20% out of the reactive power, the rest of the consumption belonging to the other installations.

The solution of placing a capacitor bank in the transformer power substation under the name of global compensation, presents an advantage only for upstream installations, exterior to the enterprise, respectively for generating, transport, and distribution installations. Using this type of compensation, the advantage represented by reactive and active power and energy losses does not appear also for enterprise installations. From this point of view, the installations from the enterprise do not benefit from the advantage given by reactive power local production.

Taking into account the importance of the contribution, given by reactive power compensation measures, also to the losses reduction in distribution installation inside the enterprise, is indicated that, for ongoing processes, to examine also the possibilities to de-centralize the banks in proper installations, that is to use with more economical compensation types, respectively, the individual or by sector consumers.

It is necessary to notice that, of special importance for consumers and electroenergetical system reactive power management, the apparition of new types of receivers, with non-linear electrical characteristics critically influence the reactive power management. The presence of the harmonic state, in many cases, determines practically the total revision of the compensation used currently, by exclusively installing the capacitor banks. This fact is determined by the reciprocal influence of these two aspects, the reactive power compensation and the harmonic, implying the application of a unique measure, respectively that of using filters that include also the existing capacitor banks.